This invention relates to certain arrangements for speech recognition.
The ability for machines to understand natural human speech has long been a goal. Great strides have been made in recent years, although it remains a difficult and computationally-intensive task. In particular, although there has been an increase in the use of speech recognition assistants on mobile devices, these typically require processing to be carried out remotely; it is currently not possible to carry out any but the most basic forms of speech recognitions using the processing power available locally on most mobile devices.
One of the factors increasing the complexity of the speech recognition problem is that of background noise. The microphones used in typical mobile devices are relatively omni-directional and will thus be sensitive to sounds from all directions (albeit not uniformly). They tend therefore to pick up background sounds (which will often include speech from others) as well as the speech which it is desired to understand.
Although better performance can be achieved using multiple microphones, this gives rise to practical problems with accommodating the additional hardware in a device. However conventional small condenser microphones are limited by the amount of inherent of ‘self’ noise which they are subject to. Condenser microphones are based on a measurement of a change in capacitance. Physical constraints (such as the maximal displacement of the membrane under high acoustic pressures) make it necessary to have a certain distance between the two plates of the capacitance (one of the plate is the microphone membrane, the other is a reference electrode situated under the membrane). This implies that the capacitance is very low, in other words the output impedance is high. In order not to short circuit this capacitance, the input impedance of the associated preamplifier must be equivalently high. High impedance will give high self-noise. A larger membrane will give a higher signal level and a higher capacitance, and thus a better signal to noise ratio (SNR) but level, while smaller area will give a lower SNR.
The present invention in its several aspects intends to provide arrangements which are beneficial in at least some circumstances in tackling the challenges facing artificial speech recognition.